Control valve system for an automatic power transmission mechanism



Oct. 3, 1967 J. J, SEARLES 3,344,681

CONTROL VALVE SYSTEM FOR AN AUTOMATIC POWER TRANSMISSION MEOHANISM FiledOct. 5, 1964 3 Sheets-Sheet 1 Oct. 3, 1967 J. J. sr-:ARLES '3,344,581

CONTROL VALVE SYSTEM FOR AN AUTOMATIC POWER TRANSMISSION MECHANISM FiledOct. 5, 1964 5 Sheets-Sheet 2 J. J. SEARLES 3,344,681 i CONTROL VALVESYSTEM FOR AN AUTOMATIC POWER TRANSMISSION MBCHANISM 3 Sheets-Sheet 3Sm/mum ms QQ m JOHN J. `SEA/W5S v INVENTOR f if Twvm Oct. 3, 1967 FiledOct. 5, 1964 United States Patent O 3,344,681 CONTROL VALVE SYSTEM FORAN AUTOMATIC POWER TRANSMISSION MECHANISM John I. Searles, Garden City,Mich., assigner to Ford Motor Company, Dearborn, Mich., a corporation ofDelaware Filed Oct. 5, 1964, Ser. No. 401,356

12 c1aims.(C1.74-47z) My invention relates generally to multiple speedratio power transmission mechanisms and automatic cont-rol valve systemsfor use there-with, and more particularly to improvements in a controlvalve system for a power transmission mechanism in an automotive vehicledriveline that includes an internal combustion engine.

This disclosure relates .to improvements in the structure disclosed inpending application Ser. No. 277,855 led by Richard .L -Leonard andRobert P. Zundel. lt relates also to improvements in my copendingapplication Ser. No. 397,798. Both of these copending disclosures areassigned to the assignee of my instant invention, and reference may behad thereto for the purpose of supplementing this disclosure.

The torque delivery elements of the power transmission mechanism of thisdisclosure include planetary gear elements, the relative motion of whichis controlled by fluid pressure operated Iclutch and brake servos. Thedriving portion of the gearing of which the planetary gear units form apart is connected to the turbine of a hydrokinetic torque convertermechanism. The impeller of the torque converter mechanism is drivablyconnecte-d in the usual fashion to the crankshaft of an internalcombustion engine in an automotive vehicle driveline. The control systemof my instant invention includes a fluid pump that is drivably connectedto torque delivery members ofthe mechanism. Suitable conduit structureis provided for hydraulically connecting the servos to the pressuresource. This conduit structure is dened in part by fluid pressuredistributor valves that selectively distribute pressure to the variousservos to condition the mechanism for operation in a -speed ratio thatis consistent with the torque transmitting requirements of thedriveline.

The system includes also a source of a pressure signal that isproportional in magnitude to the engine intake manifold pressure. Thisin general is an indication of engine torque. There is provided also asource of a pressure signal that is proportional in magnitude to thedriven speed of the driven member of the driveline. The pressuredistributor valves are adapted to respond to changes in the magnitudesof the signals to distribute control pressure to each of the servos toinitiate speed ratio changes. Y

The magnitude of the pressure that is made available to the servos isregulated by a regulator valve system that responds to changes in theoperating torque demand to vary the pressure level so that it ismaintained at all times at a value that is suflicient to establishadequate torque transmitting capacity of the clutches and brakes thatare actuated by the servos. The regulator valve system is adapted alsoto maintain an operating pressure level that will contribute to optimumshift quality. Smooth speed ratio changes are achieved and the shiftpoints occur at the `proper instant to satisfy varying performancerequirements of the driveline.

The provision of a control system of the type above set fo-rth being aprincipal object of my invention, it is another object of my inventionto provide such an automatic control valve system wherein provision ismade for personally overruling the automatic pressure distributingfunction of the distributor valves when it is desired to obtain adownshift from a high speed ratio to a lower speed ratio. I contemplatethat this downshift may occur as a driver operated downshift valve isshifted to a pressure distributing position where it is capable oftransferring an engine manifold pressure sensitive signal to anauxiliary area on the pressure distributor valves thereby changing theeffective value of the actuating forces acting upon them. This is incontrast to certain prior art arrangements that utilize the regulatedline pressure of a main fluid pressure source rather than a pressuresignal that is sensitive to engine torque or torque demand, In suchconventiinal systems the pressure signal that is distributed from thepressure source to the distributor valves during a forced downshiftoften is of a different magnitude at low vehicle speeds than at highervehicle speeds. This is due to the fact that the valve tolerance of theregulator valve system creates a back pressure at high speeds that isnot present during operation at lower speeds. At high speeds the fluidflow that must be accommodated by the regulator valve system is highersince the pressure source is in the form of a -positive displacementpump.

It is a further object of my invention to provide a valve system of thetype above set forth wherein provision is made for obtaining twodistinct drive ranges that can be selected by the vehicle operator. Inone drive range automatic speed ratio changes from an underdrive ratioto a direct drive ratio occur during acceleration from a standing start.During operation in the other drive range the vehicle may be acceleratedfrom a standing sta-rt with a low speed ratio in the driveline, and arst upshift occurs to an intermediate underdrive ratio. This is followedby a second upshift to the direct drive ratio. Selection of one driverange or the other is made by a driver controlled manual selector valve.

In the control system of the Leonard et al. application Ser. No.277,855, now Patent No. 3,295,387, pressure is distributed to anintermediate brake servo when the manual valve is shifted to one driverange position, and that same pressure is -distributed simultaneously tothe forward drive clutch servo. An automatic speed ratio change thenoccurs as the intermediate brake servo is released and the direct driveservo is applied while the forward clutch remains applied. If the manualvalve is adjusted to the other drive range position, however, pressureis distributed initially only to the forward drive clutch while an4overrunning reaction brake accommodates the torque reaction of thegearing. If the manual valve or the linkage that is used to control itis maladjusted, it is possible that pressure will be distributed acrossthe lands of the manual valve to cause an undesirable pressuredistribution to the intermediate servo when the transmission mechanismis operating in the lowest speed ratio. -Partial engagement of theintermediate brake due to the application of pressure to theintermediate servo causes premature failure of the friction elements ofthe intermediate brake and possibly other torque transmitting elementsof the system as well. It is an object of my invention to overcome thisshortcoming by incorporating in the system a bipartite fluid pressuredistributor valve that is adapted to respond to such a pressure buildupdue to leakage across the valve lands of the manual valve element. Ifsuch a pressure buildup occurs, the pressure distributor valve 'willshift to an upshift position thereby immediately conditioning thetransmission mechanism for operation in the intermediate drive range.

It is a further object of my invention to provide a valve system havin-gan accumulator feature that cushions the application of the intermediatebrake servo during a forced downshift from the high speed ratio to theintermediate speed ratio or during an upshift from the lowest speedratio to the intermediate speed ratio. lIn this way the `shift qualityis substantially improved regardless of the particular performancerequirements that may exist when the shift is initiated.

It is a further object of my invention to provide a control valve systemhaving the accumulator feature set forth in the foregoing object andwherein provision is made for modifying the accumulator action duringapplication of the intermediate brake when the pressure regulator valvesystem is conditioned for maintaining an increased line pressure.

It is another object of my invention to provide a valve system havingthe accumulator feature above set forth wherein provision is made alsofor modifying the effective accumulator action to provide a reducedaccumulator effect when ratio shifts to the intermediate ratio are madewith the engine manifold pressure at a high value.

It is a further object of my invention to provide a valve system havingthe accumulator feature set forth in the foregoing objects and whereinprovision is made for rendering the accumulator action insensitive tochanges in ambient pressure due to changes in altitude.

These and other objects and features of my invention will becomeapparent from the following description and from the accompanyingdrawings, wherein:

FIGURE l shows in schematic form the torque delivery elements of a powertransmission mechanism in an automotive vehicle driveline;

FIGURE 2A shows in schematic form a portion of an automatic controlvalve system for the structure of FIGURE 1;

FIGURE 2B shows another portion of the control valve system for thestructure of FIGURE l;

FIGURE 3 shows a detail view of the manual valve element which forms apart of the control system of FIGURES 2A and 2B; and

FIGURE 4 shows a modified accumulator valve that corresponds to theaccumulator valve of FIGURE 2A.

Referring rst to FIGURE l, numeral designates an internal combustionengine in an automotive vehicle driveline. It includes a carburetor 12which forms a part of an air-fuel mixture engine intake manifold system.The engine crankshaft for engine 10 is drivably connected to an impellerdrive shell 14 for a hydrokinetic torque converter unit 16. rThis unitincludes a bla-ded impeller 18, a bladed turbine 20 and a bladed stator22. The impeller, the turbine and the stator are situated in toroidalfluid flow relationship in the usual fashion.

A positive displacement pump 24 is connected drivably to the bladedimpeller 1S. It forms a part of the control valve system of FIGURES 2Aand 2B, as will be explained subsequently.

Stator 22 is supported by a stationary stator sleeve shaft 26 which isconnected to a stationary transmission housing shown in part at 28. Anoverrunning brake 30 for the stator 22 includes overrunning couplingelements between the shaft 26 and the stator 22 which permitfreewheeling motion of the stator 22 in the direction of rotation of theimpeller 18 although rotation of the stator 22 in the opposite directionis prevented.

The turbine 2t) is connected drivably to a central turbine shaft 32.Shaft 32 is connected directly to a clutch element 34 which is common toa forward drive friction disc clutch 36 and a reverse and directfriction clutch 38. Clutch 36, which is actuated by means of a fluidpressure operated servo, functions to connect selectively the element 34to ring gear 40 of a first simple planetary gear unit 42. Clutch 38 alsois actuated by a fluid pressure operated servo as indicated. Itfunctions to connect drivably, when it is engaged, element 34 to a driveshell 44. This shell in turn is connected to a common sun gear 46 yforplantary gear unit 42 and a second simple planetary gear unit 48.

An intermediate speed ratio friction brake band 50 surrounds the clutchdrum 52 of the reverse and direct clutch 38. Drum 52 is connected to thedrive shell 44. Brake band 50 is applied and released by means of afront intermediate brake servo 54, which includes a cylinder 56 and acooperating piston 58. Cylinder 56 and piston 58 cooperate to dene apair of opposed fluid pressure chambers-namely, a brake release chamber60 and a brake apply chamber 62. The control valve system of FIGURES 2Aand 2B functions to distribute selectively brake actuating pressure toeach chamber. The piston is connected to the brake band 50 by means ofan operator in the form of a linkage 64.

Planetary gear unit 42 includes a ring gear 66, planet pinions 68 and acarrier 70 upon which the pinions 68 are journaled. Pinions 68 mesh withring gear 66 and with sun gear 46. Carrier 70 is connected drivably to apower output shaft 72.

Planetary gear unit 48 includes a ring gear 74, planet pinions 76 and acarrier 78, the latter journaling the pinions 76. Ring gear 74 and sungear 46 are in mesh with pinions 76. Power output shaft 72 is connecteddrivably to the ring gear 74.

Carrier 78 is connected to a brake drum 80 around which is positioned areverse and low brake band 82. This brake band may be applied duringreverse drive operation and during operation in the manual low driverange by means of a fluid pressure operated reverse and low servo 84.This servo includes a cylinder 86 and a piston 88 which cooperate todene a uid pressure chamber 90. This chamber can be supplied withpressure selectively by means of the circuit illustrated in FIGURES 2Aand 2B.

The piston 88 is connected to the free end of the brake band 82 by meansof a suitable operator in the form of a linkage 92. Brake drum isconnected to the inner race 94 of an overrunning reaction lbrake 96. Theouter race of the brake 96 is connected to a portion of the transmissionhousing as shown at 98. Brake 96 includes overrunning brake elementsthat anchor the carrier 78 against rotati-on in one direction toaccommodate reaction torque, but freewheeling motion in the oppositedirection is permitted. The brake 96 is effective during operation inthe lowest speed ratio to accommodate driving torque reaction.

A compound governor valve assembly 100 is connected drivably to thepower output shaft 72. It functions in a manner subsequently to bedescribed to provide a pressure signal that is an indicator of thedriven speed of the shaft 72. Shaft 72 is connected to vehicle tractionwheels 102 through a suitable drive shaft and differential mechamsm.

To condition the mechanism for operation in the lowest speed ratio, itmerely is necessary to apply the forward clutch 36. This clutch remainsapplied during operation in an forward driving speed ratio. Torque thenis delivered from the turbine 20 and through the clutch 36 to the ringgear 40. Since the carrier 70 is connected to the power output shaft 72,and since it resists movement, sun gear 46 tends to be driven in areverse direction. A positive driving torque, however, is applied to thecarrier 7G, which is transmitted directly to the shaft 72. The reversemotion of the sun gear 46 causes ring gear 74 to be driven in a forwarddriving direction as the carrier 78 acts as a reaction member. Carrier78 is inhibited from rotation in the direction of rotation of the sungear 46 by the overrunning brake 96. Brake 96 therefore acts as areaction point for the gear system.

The positive driving torque thus transmitted to the ring gear 74 istransmitted directly to the power output shaft 72. Thus, a split torquedelivery path is provided through the gearing during low speed ratiooperation.

To condition the mechanism for intermediate underdrive operation, brakeband 50 is applied by pressurizing fluid pressure chamber 62 of thebrake servo 54. This anchors sun gear 46 so that it can function as areaction member. Turbine torque then is distributed through shaft 32 andthrough the engaged clutch 36 to the ring gear 40. Sun gear 46accommodates reaction torque as the carrier 70 is driven in a forwarddriving direction. This, of course, drives power output shaft 72 `at anincreased speed ratio as the overrunning brake 96 overruns. Thus Iatransition from the lowest speed ratio to the intermedi- `ate speedratio is accomplished by engaging only one friction torque establishingdevice-namely, the brake band 50.

To establish a high speed ratio condition, brake band 50 is released insynchronism with the application of the reverse and direct clutch 38.Clutch 36, of course, remains applied as explained previously. Thus thes-un -gear 46 becomes locked to the ring 'gear 40 and the elements ofthe gearing rotate in unison to establish a 1:1 speed ratio.

Continuous operation in the low speed range can be obtained by engagingbrake band 82. ThisV anchors the carrier 78. The forward clutch 36, ofcourse, remains applied. Turbine torque then is distributed, asdescribed previously, to the ring gear 40 as a split torque deliverypath is established in the gearing. The control system canV beconditioned so that upshifts to the higher speed ratios will beinhibited.

Reverse drive operation is obtained by releasing clutch 36 and applyingclutch 38. Brake band 82 is applied. Turbine torque then is distributeddirectly to the drive shell 44 through the apply clutch 38. This drivesthe sun gear 46 in the direction of rotation of the turbine. Sincecarrier 78 is anchored, ring gear 48 and the power output shaft 72 aredriven in a reverse direction at a reduced speed ratio. Y

During an upshift from a lower speed ratio to the'intermediate speedratio, fluid pressure is admitted to the ybrake servo chamber 62. Upon asubsequent upshift from the intermediate speed ratio to the high speedratio, pressure is distributed simultaneously to chambers 62 and 60 ofthe intermediate front brake servo 54 to release the brake 50. Upon asubsequent downshift from the high speed ratio to the intermediate speedratio, it merely is necessary to exhaust chamber 60 as the clutch 38 isreleased. The residual pressure in chamber 62 then will apply the servo54. The control system for obtaining automatic speed ratio changes inthe torque transmitting structure of FIGURE 1 is illustrated in FIGURES2A, 2B and 3. An alternate embodiment of the control system isillustrated in part in FIGURE 4.

In FIGURE 2A there is shown a main pressure regulator valve 104 which isprovided for the purpose of regulating the discharge pressure of thefront pump 24. It includes a multiple land valve spool 106 which hasformed thereon spaced valve lands 108, 110, 112 and 114. Valve spool 106is slidably situated Within a valve chamber 116, which has formedtherein internal valve lands that register with the lands 108, 110, 112and 114. Lands 108 and 110 are formed With a differential diameter todefine an annular area which is in fluid communication with a passage118, which communicates with the discharge side of the front pump 24.This passage also communicates with chamber 116 at a locationintermediate lands 110 and 112. The portion of the chamber 116intermediate lands 112 and 114 also is in fluid communication withpassage 118'as indicated.

An exhaust port 120 is formed in chamber 116 at a location directlyadjacent land 114. This port is in fluid communication with a flowreturn line 122 which communicates with the transmission sump that isdefined by the lower region of the transmission housing, not shown. Anoil screen 124 also is situated within this transmission sump and anyfluid in the sump that is delivered to the front pump passes through thescreen. The front pump supply passage is shown at 126.

Spool 106 of the main regulator valve assembly 104 is biased in anupward direction by a valve spring 128. The upper end of the chamber 116is exhausted through an exhaust port-130.

A converter feed line 132 communicates with the charnber 116 at alocation directly adjacent land 112. A transmission lubrication oilsystem shown in part at 134 communicates with passage 132. A one-waydrainback valve 136 is situated in passage 134 and is biased by a spring138 to a closed position. A pressure of approximately 5 p.s.i. willunseat the valve 136 thereby permitting distribution of lubricating oilto the lubricating system after the torque converter 16 is filled. Amaximum converter pressure relief valve 140 communicates with passage132 to prevent an excessive pressure buildup.

Located at the lower end of the valve chamber 116 is a pressure boostervalve assembly 142. It includes a valve sleeve 144 having a valve cavitywithin which is slidably positioned a pressure booster valve spool 146.This spool is formed with three spaced Valve lands 148, and 152 whichslidably register with cooperating internal valve lands formed in thesleeve 144. The lands 150 and 152 define a differential area that is influid communication with ports in sleeve 144 which in turn communicatewith a passage 154. This passage extends to the outback valve as will beexplained subsequently. The differential area of lands 150 and 152communicates also with a passage 156 which in turn extends to theintermediate band accumulator valve as will be described subsequently.

Lands 148 and 150 also define a differential area which is in fluidcommunication with a port in sleeve 144 that in turn is hydraulicallyconnected to a passage 158. The lower surface of the land 148communicates with another passage through other ports in sleeve 144.

A -valve spring 162 is situated between spool 146 and spool 106 duringoperation in certain operating zones. The regulating characteristics of'the main regulator valve 104 then are determined in part by thecalibration of both of the springs 128 and 162.

Passage 158 is pressurized, as will be explained subsequently, duringoperation of the transmission mechanism in the reverse drive range. Thisprovides a fluid pressure force that supplements the valve spring forceto cause an increased operating pressure level that is maintained by themain regulator valve 104 during reverse drive oper-ation. This increasesthe servo capacity for the reverse and low servo 84, as well as thereverse and direct clutch 38, to permit the transfer of reverse drivingtorque without slippage of the friction elements. Passage 160 on theother hand is pressurized during operation of the transmission mechanismunder coasting conditions at high vehicle speeds. An appropriate linepressure signal is made available to passage 160 by a line pressurecoasting boost valve under these conditions, as will be explainedsubsequently. During operation of the mechanism under all otherconditions, passage 160 is supplied with a throttle pressure signal thatis sensitive to the engine intake manifold pressure of the internalcombustion engine with which my improved transmission mechanism andcontrol system is adapted to be used. This also will be explainedsubsequently.

In each instance when the passage 160 is pressurized, a fluid pressureforce acting on the lower end of land 148 is created and this causes anincrease in the regulated pressure level that is maintained by theregulator valve 104. Passage 154 is pressurized by the cutback valveduring operation of the transmission mechanism at low vehicle speeds forany given engine throttle position. This pressure then causes atemporary increase in the regulated line pressure maintained by thevalve 104 as the transmission accelerates from a standing start. Afterthe speed ratio increases, however, the outback valve will exhaustpassage 154, and this will be accompanied immediately by a reduction inthe regulated pressure of valve 104. The outback in the regulatedpressure that is accompanied by a venting of the passa-ge 154 occurs asthe torque converter approaches a coupling condition and at a time priorto the automatic speed ratio changes in the gearing.

As the engine is started, pressure develops in passage 118. Thispressure acts on the differential area of lands 108 and 110 and urgesvalve spool 106 against the opposing force of the regulator valvesprings. Land 112 progressively uncovers passage 132 leading to theconverter torus circuit. This occurs prior to the time that land 114uncovers exhaust port 120.

After the converter pressure reaches a calibrated value, land 114 bringspassage 118 into fluid communication with exhaust port 120. This portcommunicates with the transmission sump through low pressure passage122.

The magnitude of the pressure level maintained in passage 118 dependsupon the calibration of springs 128 and 162 for any given valve spooldesign. This regulated pressure level can be modified, however, by thefluid pressure forces exerted on the pressure booster valve.

Passage 118 communicates with the main line pressure passage 164, whichextends to manual valve 166. A branch passage 168 extends from passage164 to the manual valve at a location spaced from the point at whichpassage 164 communicates with the manual valve.

The manual valve comprises a valve chamber 170 within which ispositioned a multiple land valve element 172. The lands for element 172are shown at 174, 176, 178 and 180, each of the lands being situated onone side only of the element 172. Other lands 182, 184, 186 and 188 areformed on the element 172 at a location that is displaced 180 withrespect to the location of lands 174 through 180.

The manual valve element 172 can be shifted to any one of severaloperating positions. These are identified by the symbols R, N, D2, D1and L, which respectively identify the reverse position, neutralposition, second drive range position, first drive range position andlow drive range position. When the element 172 assumes the positionshown, passages 164 and 168 are blocked by land 184 and land 170,respectively.

A passage 190 extends from the manual valve chamber 170 to the 1-2 shiftvalve assembly, which will be described subsequently. Passage 192communicates with the manual valve chamber 170 at a location directlyadjacent passage 190. Passage 194 communicates with valve chamber 170 ata point directly adjacent passage 192. The space between lands 178 and176, when the manual valve element 172 assumes the position shown inFIG- URE ZB, establishes fluid communication between passages 190, 192and 194. This space also is in fluid communication through the manualvalve element 172 with the space between land 182 and land 184.

An exhaust port 196 communicates with the valve chamber 170 at alocation adjacent land 184. Passage 158 which extends to the pressurebooster valve as explained previously communicates with the chamber 170at a location adjacent the right-hand end thereof. The passage 198communicates with the chamber 172 at a location intermediate exhaustport 196 and passage 158.

If the manual valve element 172 is shifted to the reverse drive positionR, passages 190, 192 and 194 are exhausted through the left-hand end ofthe chamber 170. Passage 164 is blocked by land 184. Passage 168, whichreceives pressure from the main line pressure passage 164, is in uidcommunication with passage 198 which extends to the reverse and lowservo 84 through the 1-2 shift valve assembly as will be explainedsubsequently. Passage 158, which extends to the pressure booster valveand to the reverse clutch 38, is in fluid communication with passage 198through a space intermediate lands 186 and 188.

If the manual valve element 172 is shifted to the D2 position, thetransmission mechanism will be conditioned for acceleration from astanding start in the intermediate speed ratio. A subsequent upshift mayoccur, as will be explained subsequently, in response to movement of the2-3 shift valve. Passage 190 is brought into fluid communication withpassage 164 through the valve element 172 and is pressurized. Thiscauses the 1-2 shift valve element to assume an upshift position.Pressure then is distributed under these conditions from passage 164 andthrough the valve element 172 to the passage 194, which is in fluidcommunication with the forward clutch servo 34 and the apply side 62 ofthe intermediate brake servo 54. Passage 192 is pressurized in the samefashion so that pressure may be distributed to the 2-3 shift valve thusconditioning it for subsequent upshift to the direct drive ratio.Passages 198 and 158 both are exhausted through the exhaust port 196.

If the manual valve element 172 is shifted to the D1 position, thetransmission is conditioned for acceleration from a standing start inthe lowest speed ratio and two subsequent upshifts then will -beavailable. Under these conditions passage 190 is exhausted through thelefthand side of the manual valve chamber 170. Passages 198 and 158remain exhausted although they are exhausted through the right-hand endof the manual valve chamber rather than through the exhaust port 196.Thus the only change in the pressure distribution during movement of themanual valve element 172 from the D2 position to the D1 position occursas passage 190 becomes exhausted.

If the manual valve element 172 is shifted to the L position, thetransmission will be conditioned for continuous operation in the lowestspeed ratio as the vehicle accelerates from a standing start. Noupshifts will be available. If the shift is made while the vehicle isunder motion at a speed greater than a calibrated minimum value,however, a downshift will occur to the intermediate speed ratio and thetransmission will operate continuously in that ratio until the vehiclespeed falls below the predetermined value. At that time a downshift tothe lowest speed ratio will occur and the transmission thereafter willbe locked in the lowest speed ratio and no upshifts can occursubsequently.

When the manual valve assumes the L position, passages and 192 areexhausted through the left-hand end of the manual valve chamber 170.Passage 164 is blocked by land 182. Passage 194 is pressurized as it isbrought into communication with passage 168 by means of the spacebetween lands 176 and 178. Exhaust port 196 is blocked by land 184 andpassage 198 is brought into fluid communication with passage 168.Passage 158 is exhausted through the right-hand end of the valve chamber170.

The various operating positions of the manual valve element 174 aredetermined by a spring loaded detent mechanism that comprises a plunger200 located in the valve body in a cooperating bore. Plunger 200 has arounded nose that engages detent recesses 202 formed in the valveelement 172. Each recess 202 corresponds to one of the operatingpositions described in the foregoing paragraphs.

A 1-2 shift valve assembly is shown in FIGURE 2A. It comprisestwo/separate valve elements 204 and 206 which are positioned within acommon valve chamber 208. Valve element 204 comprises spaced annularvalve lands 210, 212, 214 and 216. Valve element 206 comprises two valvelands of differential diameter, as shown at 218 and 220. The annulararea dened by the differential diameter valve lands 218 and 220 is influid communication with a modulated throttle pressure passage 222 whichis pressurized with a modulated pressure signal that is proportional inmagnitude to engine intake manifold pressure as will be explainedsubsequently. The portion of the chamber 208 intermediate the lands 218and 216 is in fluid communication with passage 190. If the manual valvehappens to be maladjusted, or if the driver controlled linkage mechanismfor adjusting the valve element 172 is maladjusted, it may be possiblefor passages 192 and 190 to become pressurized imultaneously. Forexample, if it is desired to operate in the D1 range and the valveelement 172 assumes, due to miscalibration or maladjustment, a positionintermediate the D1 and D2 positions, it is possible for passage 190 tobecome pressurized. Under these conditions a pressure buildup wouldoccur on the top of 9 Valve land 216 thereby forcing the valve element204 to assume an upshift position so that the transmission will operatein the intermediate drive range. By connecting passages 190 and 222through valve chamber 208, partial application of the intermediate servoduring operation in the D1 range thus is avoided. This is a safetyfeature that prevents inadvertent simultaneous operation of thetransmission mechanism in the D1 range and the D2 range as the vehicleaccelerates from a standing start.

Valve elements 204 and 206 are biased in an upward direction, as viewedin FIGURE 2A, by a valve spring 224. Valve element 210 is formed with aslightly smaller diameter than the diameter of valve land 212. When thevalve element 204 assumes the position shown, it communicates with apassage 226 which extends directly to the forward drive clutch servo.This passage is pressurized by passage 194 with which it communicates.The resulting pressure force acting in an upward direction on t-he valveelement 204, a viewed in FIGURE 2A, supplements the action of the valvespring 224. When the valve element 204 assumes a downward position,however, the annular area defined by the valve lands 210 and 212 isbrought into fluid communication with a passage 228 which in turncommunicates with an exhaust port 230 formed in the valve chamber 208.This communication with the exhaust port is established, however, -onlywhen the valve element 204 assumes a downward position. When the valveelement 204 is in an-upward position as shown in FIG- URE 2A, the valvechamber 208 establishes communication between passage 198 and passage228 while the eX- haust port 230 is brought into communication withpassage 232, the latter communicating with the apply side of theintermediate brake servo. Upon a shifting movement of the Valve element204 in a downward direction, communication between exhaust port 230 andpassage 232 is interrupted while communication between passage 232 andpassage 226 is established. The latter passage is pressurized wheneverthe manual valve is shifted to any one of the forward driving positions.

The upper end of land 220 is subjected to a governor pressure signalthat senses the vehicle speed. Pressure is distributed to this landthrough a governor pressure passage 234. This passage in turncommunicates with the governor valve assembly that will be describedsubsequently.

When the manual valve assumes the L position, passage 198 is pressurizedand when the vehicle is standing or when it is operating at very lowspeeds, passage 198 communicates directly with passage 228 through thevalve chamber 208. Thus the reverse and |low servo 84 becomes applied.As an upshift occurs, land 216 blocks passage 198 and passage 228becomes exhausted through port 230' as explained previously.

Automatic upshifts from the intermediate drive ratio to the direct drivehigh speed ratio are controlled by the 2-3 shift valve assembly whichcomprises a multiple land valve spool 236 which is situated slidablywithin a valve chamber 238. It includes a valve land 240, a valve land242, a valve land 244 and a valve land 246. Valve spool 236 is urged inan upward direction by a valve spring 248. Governor pressure acts uponthe upper end of land 240 and is distributed thereto through governorpressure passage 234. Passage 192, which is pressurized during operationin either the D1 or D2 ranges, is in fluid communication with chamber238 at a location intermediate lands 242 and 244. Land 242 is slightlylarger than land 244 and a pressure force acting in an upward directionthus is established when the valve element 236 assumes the positonshown. When the valve element 236 is moved downwardly, however, the areadefined by these differential diameter valve lands is brought into fluidcommunication with passage 250 which is exhausted through passage 158.Thus movement of the valve element 236 in a downward direction isaccompanied by a snap action due to the change in the balanced forcesthat act upon it.

In this respect the movement of the 2-3 shift valve element is similarto the movement of the 1-2 shift valve element 204 Where thedifferential diameter valve lands 212 and 210 are pressurized in the lowspeed ratio position but exhausted in the intermediate speed ratioposition. Movement of the valve element 204 also is accompanied by asnap action. This produces a hysteresis effect which eliminates huntingof the shift valve elements. Following movement of the valve elements tothe upshift positions, a corresponding downshift does not occur untilthe vehicle speed reaches a value that is less than the value at whichthe upshift occurs for any given engine intake manifold pressure.

The reverse and direct drive clutch 38 is exhausted through the 2 3shift valve element when the latter assumes the position shown in FIGURE2A. The exhaust llow path for the reverse and direct clutch isestablished by passage 252, which communicates directly with the directdrive clutch servo, passage 254 and passage 250, the latter beingconnected directly to the exhausted passage 158. When the valve element236 assumes a downward position, however, passage 254 is brought intocommunication with passage 192 thereby causing pressure distribution tothe reverse' and direct drive servo.

Modulated throttle pressure passage 222 communicates with the lower endof the valve land 246 to supplement the action of the spring 248. Thispassage 222 receives its pressure from the throttle modulator valvewhich includes a single diameter valve element 256 situated in the lowerregion of the valve chamber 238. Spring 248 is disposed between element256 and the element 236. The 4output signal of the throttle boostervalve 294 is distributed through a passage 258 to the lower end of theelement 256. This pressure in passage 258 is related in magnitude to theengine intake manifold pressure. At a manifold pressure less than apredetermined value the signal in passage 258 is not sufficient toovercome the opposing force of spring 248. At any manifold pressure inexcess of that value, however, the spring pressure of spring 248 isovercome thereby permitting a reduced or modulated pressure to enterpassage 222. Thus the minimum throttle upshifts points are establishedindependently of manifold pressure. The shift points depend only uponthe calibration of the springs for the shift valves and upon thegovernor pressure force acting upon the shift valves. When a shiftoccurs under advanced throttle operating conditions, the valve elements236 and 204 move in response to the forces established by the governorpressure signal and the manifold pressure repsonsive signal.

As shown in FIGURE 2B, the manifold pressure sensitive signal isproduced by the primary throttle valve and vacuum diaphragm assemblyillustrated in FIGURE 2B.

The primary throttle valve comprises a valve spool 260 having formedthereon spaced valve lands 262, 264 and 266. These lands slidablycooperate with internal valve lands formed in `a throttle Valve chamber268. Line pressure passage 164 communicates with chamber 268 at alocation adjacent land 264. An exhaust port 270 communicates with thechamber 268 at a location `adjacent land 266. A primary throttlepressure passage 272 communicates with the chamber 268 at a locationintermediate eX- haust port 270 and line pressure passage 164. Thepressure in passage 272 is transferred to the left-hand end of ltheelement 260 and acts against the face of land 262, a suitable internalpass-age 274 being provided for this purpose.

The vacuum diaphragm comprises a diaphragm housing 276 and a diaphragmhousing 278. They are secured together by crimping as shown at 280. Aexible diaphragm 282 is secured at its margin to the housings 276 and278 at the juncture 280. A diaphragm element 284 secured to the centralregion of the diaphragm 282 carries diaphragm backup discs on eitherside of the diaphragm 282 as indicated. A valve operating stem 286 issituated between the member'284 and the valve element 260.

Housing 276 is secured to a threaded member 28S which is threadablyreceived within the valve body. The housing 278 and the diaphragm 282dene a pressure cavity which is in fluid communication with a fitting290. This fitting provides a connection with an intake manifold pressurepassage 292.

A spring 293 is situated between the diaphragm 282 and the end of thehousing 278 and urges the diaphragm 282 in a left-hand direction.Atmospheric pressure exists on the left-hand side of diaphragm 282. Thuswhen a manifold vacuum exists in the engine intake manifold system, thespring 293 and the differential pressures acting upon the diaphragm 282create a balanced condition. Upon an increase in manifold pressure, thevalve element 260 will tend to be urged in a left-hand direction. Theconverse is true upon a decrease in manifold pressure.

The valve element 260 modulates the pressure in passage 164 and producesa resultant signal in passage 272 that is an indicator of the magnitudeof the manifold pressure in the chamber on the right-hand side of thediaphragm 282.

The signal in passage 272 is distributed to the throttle booster valve294. This valve includes a valve element 296 which has formed thereonspaced valve lands 298 and 300. Land 300 is formed with a largerdiameter than land 298.

Element 296 is slidably situated within a valve chamber 302 which isformed with internal valve lands that register with lands 298 and 300.Passage 272 communi- Cates with chamber 302 on either side of the land300.

Main line pressure passage 164 communicates with the valve chamber 302through a passage 304, the degree of communication being controlled byland 298. Passage 258 which is the throttle booster valve outputpassage, communicates with the chamber 302 at a location intermediatepassage 304 and passage 272. Valve element 296 is urged in a right-handdirection as viewed in FIGURE 2B by a valve spring 306.

When the engine intake manifold pressure is less than a predeterminedvalue (high vacuum), valve element 296 assumes the position shown. Thethrottle pressure in passage 272 under these conditions is insufficientto cause the element 296 to shift in a left-hand direction. Thus passage272 communicates directly with passage 258, and the throttle modulatorvalve then is subjected directly to the output signal of the primarythrottle valve. When the magnitude of the engine intake manifoldpressure exceeds a calibrated value (low vacuum), however, the spring306 yields thereby permitting controlled communication between passages258 and 304. At the same time the degree of communication betweenpassage 258 and passage 272 becomes reduced. Thus the line pressure inpassage 304 is used to augment the signal in passage 272 to produce amagnified output signal in passage 258 at advanced engine carburetorthrottle settings and low vacuum. The magnitude of the signal in passage258 then is made to correspond more closely to actual engine torquedemand of the operator. Normally the engine intake manifold pressurechanges only slightly upon a change in engine throttle position once theengine throttle setting has exceeded a median value. A torque demanddownshift then would be difficult to achieve at advanced engine throttlesettings if it were not for the fact that the throttle booster valvefunctions during operation -at advanced engine throttle settings toboost the output signal of the primary throttle valve. The calibrationof the primary throttle valve and the throttle booster valve thusdetermine the shift points for any given governor pressure.

The automatic controlling functions of the 1-2 shift valve and the 2-3shift valve can be overruled by the downshift valve 308. This valvecomprises a valve element 310 having spaced valve lands 312 and 314which register with internal valve lands formed in the downshift valvechamber 316. Valve element 310 is urged in a left-hand direction byvalve spring 318. Passage 258 communicates with chamber 316 at alocation directly adjacent land 314.

lt normally is blocked by land 314 when the engine carburetor throttlesetting is at any value other than a position that corresponds to apoint beyond the wide open throttle position. The valve element 310 isconnected mechanically to the engine carburetor throttle with a lostmotion linkage. It is insensitive to engine carburetor throttle valvemovement except in those instances when the carburetor throttle valve ismoved beyond the wide open throttle setting. Thus whenever the enginecarburetor throttle setting is at a position less than that which wouldcause a shifting movement of the element 3'10, passage 320 is exhaustedthrough passage 322, the latter communieating with passage 198.Exhausted passage 198 communicates with passage 324.

Passages 320 and 322 communicate with the chamber 316 at a locationintermediate lands 312 and 314.

When a forced downshift is desired, the operator advances the enginecarburetor throttle to its maximum setting. At this time the effectivepressure signal in passage 258 is at a maximum. Thus when element 310 isshifted in a right-hand direction, communication is established betweenpassages 258 and 320 so that the maximum signal of the throttle boostervalve is distributed to passage 320 and to the 2-3 shift valve assembly.This signal supplements the action of the spring 248 to urge the spool236 in an upward direction. The same signal is distributed to thedifferential `area defined by the lands 218 and 220 of the 1-2 shiftvalve assembly. Thus each shift valve assembly is urged to its downshiftposition. If the vehicle speeld at this time is lower than apredetermined value, a downshift will occur. Each shift valve assembly,of course, has its `own governor pressure beyond which a downshiftcannot be effected by the downshift valve 308.

This downshift valve assembly is unlike conventional downshift valvearrangements in automatic control valve circuits of known construction.It is conventional practice to employ a downshift valve that is in fluidcommunication with the regulated line pressure passage that wouldcorrespond to passage 3164. When the downshift valve in sucharrangements is actuated, communication between the shift valveassemblies and the exhaust regions is interrupted and communicationbetween the shift valve assemblies and the main regulated line pressurepassage is established. If at that time the engine speed is operating ata relatively high value, a large ow from the engine driven pump must beaccommodated by the regulator valve assembly. It is difficult for theregulator valve assembly to maintain a constant regulated pressure asthe How increases from a low value to the maximum value. A slightincrease in the regulated pressure level thus will occur as the enginespeed increases. This is due in part to the dimensional tolerances ofthe regulator valve assembly and the pump itself. It has been found,therefore, that in such conventional arrangements the shift pointscannot be established accurately upon a forced downshift. This is due tothe fact that the signal that is distributed to the shift valve assemblyby the downshift valve is not of a known value since it is variable anddependent in part upon engine speed. In my improved downshift valveassembly, however, the downshift valve element is supplied withregulated pressure-namely, primary throttle valve output pressure or,more accurately, throttle booster valve output pressure. The magnitudeof this output pressure is independent of the engine speed. Thus thedownshift points are established with more precision than they would beif the conventional downshift valve arrangement were employed.

The governor valve assembly for producing the road speed sensitivesignal comprises a valve body having formed therein a primary governorvalve chamber 3126 and a secondary governor valve chamber 328. A primarygovernor Valve element 330 is situated in chamber 326 and correspondingsecondary governor valve element 332 is situated in chamber 328. Element330 includes valve 13 lands 334 and 336, which register with internalvalve lands formed in the chamber 326. A primary governor valve spring338 normally urges the valve element 330 radially inwardly. The radiallyoutward region of chember 326 is exhausted through an exhaust port 340.

The secondary governor valve element 332 includes valve lands 342 and344, the latter being formed with a larger -diameter than the former.The radially inward region of the chamber 32S is exhausted through aneX- haust port 346.

Passage 194, which is pressurized during operation in the forward driveranges, is in fluid communication with passage 34'8 which extends to thechamber 328 at a location directly adjacent land 342. The outputpressure signal passage 234 communicates -with the secondary valvechamber 328 at a location directly adjacent land 344. The radiallyoutward end of land 342 is in fluid communication with the primarygovernor valve chamber 326 at a location intermediate lands 334 and 336,a suitable cross passage 350 being provided for this purpose. A spring352 urges element 332 radially outwardly.

When pressure is distributed to passage 348, valve element 332 tends tomove radially inwardly. This causes passage 234 to be brought intocommunication with eX- haust port 346, and communication between passage234 and passage 348 is interrupted. At the same time passage 348 isbrought into communication with the radially outward end of the land342. As the power output shaft for the transmission mechanism beings torotate, a centrifugal force develops on the valve element 330 due to itsmass and its operating radius. At a predetermined breakpoint speed,valve element 330` will move outwardly against the opposing force ofspring 3318 thereby exhausting passage 354) through exhaust port 340.This relieves the pressure on the radially outward end f land 342 so thesecondary governor valve element beings to modulate and to produce yapressure signal in passage 234 that is related functionally in magnitudeto the speed of rotation of the power output shaft.

To cushion the application of the direct drive clutch when a 2 3 upshiftis made under minimum throttle conditions, there is provided a 2-3backout valve. This has been described in the copending Leonard et al.application Ser. No. 277,855, `and reference may be had thereto for thepurpose of supplementing this disclosure. The backout valve includes avalve element 354 having spaced annular valve lands 356 and 358. Theseare slidably situated ywithin a valve chamber 360 which is formed withinternal valve lands that register with the lands 3'5'8 and 356. Valveelement 354 is urged in an upward direction as viewed in FIGURE 2B byvalve spring 362. The upper end of the chamber 360 is in fluidcommunication with the reverse and direct drive clutch through a passage364. Passage I232 which was discussed with reference to the 1-2 shiftvalve assembly, communicates with the Valve chamber 360 at a locationintermediate lands 356 and 358. Passage 367, which extends to the applyside of the lintermediate brake servo, communicates with the chamber 360at a location directly adjacent land 358. When the element 354 assumesthe position shown, Valve chamber 360 establishes iiuid communicationbetween passages 232 and 367.

If an upshift from the intermediate speed ratio to the direct drive highspeed ratio occurs under 4minimum throttle conditions,rthe 2-3 shiftvalve assembly will cause pressure to be distributed to passage 254 frompassage 192 as the valve element 236 moves downwardly from `the positionshown in FIGURE 2A. This will cause a pressure buildup in the reverseand direct drive servo. This pressure buildup is distributed also to theupper end of the land 358 through passage 364. At the same time thepressure buildup begins to occur on the olfside of the intermediatebrake servo as pressure is distributed from passage 252 to passage 366through one-way check valve 365. The pressure in line 364 in directdrive from line 192 is the same as the pressure in line .232 in allforward drive ranges from line 194. At some predetermined point duringthe pressure buildup, spool 354 -moves downwardly against the opposinginfluence of spring 362 thereby bringing passage 364 into fluidcommunication with passage 367, which extends to the apply side of theintermediate brake servo. The direct drive clutch will become locked upunder these minimum throttle conditions at a very low pressure. Thebackout valve is designed to modify the servo capacity of theintermediate brake servo during the shift interval so that the end pointor point at which the intermediate brake servo will become released willcorrespond to the point at which the direct drive clutch will becomelocked up. Under Zero throttle conditions, these end points shouldcoincide and no substantial degree of overlap should occur. On the otherhand if a throttle pressure is present in passage 272, the transmissionat that time is -delivering torque although at a reduced magnitude.Under these conditions the shifting of the valve spool 354 in Iadownward direction will be delayed until the pressure in passage 364 andin the reverse and direct drive clutch will have reached a higher value.Thus the apply side of the intermediate brake servo is brought intofluid communication with the reverse and direct drive clutch at a latertime during the shift interval. Finally, when a 2-'3 shift occurs underintermediate or high tor-que conditions, the throttle pressure inpassage 272 is suicient to maintain the valve element 354 in an upwardposition until after the direct drive clutch becomes fully engaged andthe intermediate servo becomes released. If it shifts thereafter, it hasno influence upon the shift quality and has no function.

In order to make certain that the 2-'3 backout valve will assume anupward position during manual low operation, a manual low valve 368 isprovided. It is necessary that the valve element 354 be held in anupward position since it would be impossible to pressurize the applyside of the intermediate servo if passage 367 were in continuous uidcommunication with passage 364. The latter, of course, is exhaustedthrough the 2-3 shift valve assembly and passage 250. The passage 250 inturn communicates with exhausted passage 2158. Thus the lower end of themanual low valve 368 is pressurized. As the manual valve is shifted tothe L position, pressure is distributed to the manual low valve throughpassage 324.

As explained in an earlier part of this specification, it is necessaryto reduce the magnitude of the regulated line press-ure that ismain-tained by the main regulator valve after the speed ratio increasesto an intermediate value. It is desirable that this occur at a timeprior to the point at which an automatic upshift would occur. Thisoutback is accomplished lby the cutback Valve shown at 370 in FIGURE 2B.This valve includes a Valve element 372 which is situated slidablywithin a valve chamber 374. Element 3712 includes three spaced valvelands 376, 378 and 38u. An exhaust port 382 communicates with the lowerregion of the chamber 374. The upper region of the chamber 374 is influid communication with governor pressure passage 234. Throttlepressure passage 272 communicates by means of a branch passage 384 withthe chamber 374 at a location intermediate lands 376 and 380. The`diameter of land 376 is greater than the diameter of land 380, so thepressure force due to the throttle pressure in passage 272 normallyurges the cutback valve element 372 in an upward direction as viewed inFIGURE 2B. This force is opposed by the oppositely directed force due tothe governor pressure in passage 2'34.

When the valve element 372 is positioned as shown, throttle pressure isdistributed through chamber 374 from passage 27.12 to outback pressurepassage 386. On the other hand when the valve element 372 assumes adownward position, passage 336 is brought into fluid communication withexhaust port 38-2. The speed at which passage 386 because exhausted thendepends in part upon the magnitude of the throttle pressure in passage272. At advanced engine throttle settings, the cutback in pressureoccurs at a higher vehicle speed following acceleration from a standingstart.

As explained previously the cutback pressure is distributed from passage386 to passage 154, which in turn communicates with the annular areadefined by the differential diameter lands 150 and 152 of the pressurebooster valve assembly. This same pressure is distributed throughpassage 156 to the intermediate band accumulator valve 388. This valvecomprises a valve spool 390 having spaced lands 392 and 394. These landsare slidably situated within a valve chamber 396 which defines internalvalve lands that register with the lands 392 and 394. Valve spool 390 isbiased in a downward direction, as viewed in 4FIGURE 2A, by a valvespring 398. The lower region of the chamber 396 is in fluidcommunication with passage 198 through a branch passage 400. Thus whenthe imanual valve is shifted to the reverse drive position or to the lowdrive range position L, passage 400 becomes pressurized and valve spool390 is urged in and upward direction against the opposing influence ofspring 398 and is rendered ineffective. The accumulator valve 388functions only when the passage 400 is exhausted.

Passage 366, which communicates with the release side of theintermediate brake servo, communicates with the valve chamber 396 at alocation intermediate lands 392 and 394. Passage 252, which extends tothe direct drive clutch, communicates with the chamber 396 at a locationabove land 394. Valve element 390 establishes communication betweenpassages 366 and 25l2 when it shifts upwardly against the opposinginfluence of spring 398.

The force of spring 398 can be supplemented by a fluid pressure forcethat acts upon the upper end of a single diameter valve element 402which is slidably situated within a sleeve 404 disposed in a largediameter portion of chamber 396. The passage 156 distributes pressure tothe upper end of element 402 when the cutback pressure passage 154 ispressurized.

If we assume for the moment that passage 156 is exhausted and thetransmission is conditioned for a 1-'2 upshift during the accelerationperiod, the intermediate brake servo 50 will become pressurized due todistribution of pressure to passage 367. This causes the intermediateservo piston to stroke, and the fluid that exists on the release side ofthe intermediate brake servo is displaced through passage 366. Theoutlet for this fluid in passage 366 is temporarily blocked by theaccumulator valve element 390. When the back pressure thus developed inpassage 366 reaches a value of approximately 10 p.s.i., spring 398yields thereby permitting the fluid in passage 366 and on the releaseside of the intermediate brake servo piston to `become exhausted throughpassage 252 and hence through the 2-'3 shift valve assembly to passage250. It then is exhausted through the exhausted passage 158. This backpressure in the intermediate servo cushions the application of theintermediate brake band and thus softens the 1-2 shift. Thissubstantially improves the shift quality.

As explained previously the cutback valve is shifted at a time prior tothe 1-2 upshift during acceleration from a standing start. Thus theaccumulator valve can be calibrated in such a way that it it willfunction in the ldesired fashion with the pressure in passage 156 at avalue of zero. The back pressure that is developed on the release sideof the intermediate brake servo thus is a function `only of thecalibration of spring 398.

If we continue to assume that passage 156 is exhausted, the intermediateband accumulator valve will function in a similar fashion to cushion theapplication of the intermediate brake band during a 3-2 downshift. Underthese conditions the direct drive clutch becomes released as passage 252and passage 254 become exhausted through the 2-3 shift valve assembly.At the same time the uid on the release side of the intermediate servotends to accumulate as the intermediate servo piston begins to stroke.This 16 again develops a back pressure in passage 366. When the backpressure reaches a value of approximately l0` p.s.i., the spring 398yields thereby permitting the fluid on the release side of theintermediate servo to be exhausted through passage 252 just as it doesduring a 1-2 upshift.

When the 3-2 downshift is initiated at low vehicle speeds and withadvanced engine throttle settings, it is possible for the cutback valveto assume the position shown in FIGURE 2B rather than the downwardposition. In a preferred embodiment of the invention, the cutback valvewill move to the position shown under wide open throttle operatingconditions Whenever the vehicle speed is less than 30 m.p.h. If this isthe case, of course, passage 154 and passage 156 will be pressurized.The magnitude of the regulated line pressure is boosted due to theaction of the pressure booster valve as explained previously. Also, thespring force of spring 93 is augmented by the pressure force acting uponvalve element 402. Thus when a 3-2 downshift occurs, the stroking of theintermediate servo piston creates a higher back pressure than it wouldotherwise.

In a preferred embodiment of my invention the back pressure produced inpassage 366 upon a 3-2 downshift at low speeds and advanced throttlesettings is approximately 30 p.s.i. This higher back pressure isnecessary in order to produce the required cushioning action under suchtorque delivery conditions. Of course, the total effective servo forcedue to the pressure differential in each of the two opposed fluidpressure chambers of the intermediate servo is much higher under theseconditions than it would be under operation at reduced engine throttlesettings notwithstanding the fact that the back pressure in passage 366is higher. This is due to the augmentation in the regulated lineIpressure level due to the action of the pressure booster valve. It isapparent, therefore, that the calibration of the accumulator valve canbe tailored so that it will satisfy the requirements of a 3-2 downshiftunder advanced throttle speed conditions without reference to thecalibration that is necessary for a high quality 1-2 upshift. Theaccumulating action, of course, is apparent during each shift. However,the degree of accumulation can be modified to satisfy the peculiarrequirements of each shift.

If a 3-2 downshift occurs at higher vehicle speeds at reduced throttlesettings, the cutback valve will shift to the cutback position at a timeprior to the 32 downshift. Under these conditions the accumulator valvefunctions in the same fashion as it does during a 1-2 upshift. A higherdegree of accumulating action is not required under these circumstances.

Another desirable characteristic of the intermediate band accumulatorvalve is its automatic compensation for altitude changes when thevehicle is operated at sea level and the valve system is calibrated sothat it will respond properly to a given primary throttle pressure. Toproduce the necessary shift points, the calibration will beinappropriate for corresponding operation at increased altitudes. Theengine intake manifold pressure, of course, is sensitive to altitudechanges. A greater engine throttle setting is required to produce agiven manifold pressure at an increased altitude than the correspondingsetting that would be required to produce that same pressure at sealevel. The shift points are affected accordingly. The calibration of theintermediate band accumulator valve, however, is not affected by thesechanges in altitude lsince the same change in the throttle pressure thatis sensed by the shift valve is sensed also by the valve element 402.

Primary throttle pressure is distributed through passage 272 to the linepressure coasting boost valve 406. This valve comprises a valve spool408 having spaced valve lands 410 and 412. Spool 408 is biased in anupward direction, as viewed in FIGURE 2A, by valve spring 414. Passage272 communicates with a passage 416 through the line pressure coastingboost valve chamber 418 within which the spool 408 is situated. Chamber418 is formed with internal valve lands that cooperate with lands 412and 410. Line pressure passage 164 communicates by means of a branchpassage 420 with the chamber 418 at a location intermediate lands 410and 412. Governor pressure from passage 234 is distributed to the upperend of chamber 418. It acts upon land 410 to produce -a governorpressure force that opposes the influence of spring 414.

When the transmission mechanism is operated under torque, the throttlepressure in passage 272 is sufficient to maintain the valve spool 408 inthe position shown in FIGURE 2A. If, however, the vehicle is coastingunder zero or minimum throttle conditions and if the vehicle speed isgreater than a predetermined value, valve spool 408 will be shifted in adownward ldirection thereby establishing uid communication between linepressure passage 164 and passage 416 which in turn communicates withpassage 160 described in the preceding part of the specification. Thisproduces a boost in the magnitude of the regulated line pressure therebymaking it possible for the clutch and brake servos to maintain capacityduring coasting at high speeds. At lower speeds the governor pressure inpassage 234 is insufficient to overcome the opposing influence of spring414 regardless of whether any throttle pressure in passage 272 exists.Under these conditions the line pressure boost does not occur duringcoasting oper-ation.

Referring next to FIGURE 4, I have shown a modified form` of theintermediate band accumulator valve. In FIGURE 4 the valve assemblyitself can be formed in an identical fashion. Passage 400 of FIGURE 2A,however, is replaced in FIGURE 4 by a passage 422 which communicateswith passage 222 of the 1-2 shift valve assembly. It thus will beapparent that on a 1-2 upshift or a 3-2 downshift, the calibration ofthe accumulator valve will be dependent upon the magnitude of themodulated T.V. pressure in passage 422 as well as upon the calibrationof the valve spring 398. Each of the elements of the valve assembly ofFIGURE 4 have been identified with reference characters that areidentical with the corresponding reference characters of FIGURE 2Aalthough primed notations have been added.

If a 1-2 upshift occurs when the magnitude of the primary throttle valvepressure is insuflicient to shift the throttle modulator valve, thepressure in passage 422 will be zero and the valves of FIGURE 4 thenwill function in the same fashion as the corresponding valves of FIG-URE 2A. If a 1-2 shift occurs with an advanced engine throttle setting,however, the magnitude of the throttle pressure that is developed willbe sufficient to produce a modulated throttle pressure in passage 222and in passage 422 and the accumulating action of the accumulator valvewill be modified accordingly as a shift occurs. With increasing enginethrottle settings, the accumulating action washes out and at some valueat which passages 366 and 252 are brought into fluid communication, theaccumulating action is zero. Thus the effective back pressure that isdeveloped as the intermediate servo piston strokes can be any valuebetween zero and l p.s.i. on a 1-2 upshift with advanced engine throttlesettings. This introduces another variable that can be adjusted tofurther improve the shift quality on a 1-2 upshift.

The same influence of modulated throttle pressure in passage 422 can bemade effective also upon the 3-2 downshift. Thus the pressure in passage422 on a 3 2 downshift opposes the influence of spring 398. As explainedpreviously, if a 3-2 downsh-ift occurs at an advanced engine throttlesetting and at reducedspeed, the cu-tback valve will have caused thevalve element 402 to become pressurized. This normally would tend toproduce a back pressure of a magnitude of about 30 p.s.i. But themagnitude of this back pressure is reduced as the throttle pressure inpassage 422 increases. Thus the effective back pressure can be any valuebetween zero and 30 p.s.i. This, as in the case of the 1-2 upshiftprovides another variable that can be used to more precisely tailor theshift points to produce any desired shift quality.

Having thus described preferred embodiments of my invention, what Iclaim and desire to secure by U.S. Letters Patent is:

1. In a control system for a power transmission mechanism adapted todeliver driving torque from a driving -rnember to a driven member, gearelements forming plural torque delivery paths between said drivingmember and said driven member, fluid pressure operated servo means forcontrolling the relative motion of said gear elements, a fluid pressureoperated clutch actuated by one servo means for connecting together twoelements of said gearing to establish a high speed ratio condition,fluid pressure operated brake means actuated by said other servo meansfor anchoring an element of said gearing to establish a relatively lowspeed ratio condition, said brake servo means comprising a fluidpressure cylinder, a piston in said cylinder cooperating therewith todefine a pressure release chamber land a pressure apply chamber, a Huidpressure source, conduit `structure interconnecting said pressure sourceand each chamber of said brake servo and connecting also said sourcewith said clutch, fluid pressure distributor valve means in said conduits-tructure Vfor distributing pressure selectively from said source tosaid clutch and to said brake servo chambers', said brake servo assuminga released condition when both chambers thereof are pressurized andassuming an applied condition when one chamber thereof is pressurized asthe other chamber thereof is exhausted, a fluid pressure passagecommunicating with said other chamber, a portion of said fluid pressuredistributor valve means being disposed in said passage and adapted toselectively pressurize and exhaust the same, an accumulator valvesituated in said passage comprising a movable valve element and a valvechamber that receives said valve element, said valve chamber defining inpart said passage, and -meaus for biasing said valve element to apassage closing position, said piston developing a back pressure as saidbrake servo becomes applied, said accumulator valve including pressureresponsive means for urging the valve element to a passage openingposition in response to a pressure buildup in said other servo chamberand said passage, the application of Asaid brake servo thereby beingcushioned.

2. In a control system for a power transmission mechanism adapted todeliver driving torque from a driving member to a driven member, gearelements forming plural torque delivery paths between said drivingmember` and said driven member, fluid pressure operated ser'vo means forcontrolling the relative motion of said gear elements, a fluid pressureoperated clutch actuatedby one servo means for connecting together twoelements of said gearing to establish a high speed ratio condition,fluid pressure operated brake means actuated by said other servo meansfor anchoring an element of said gearing to establish a relatively lowspeed ration condition, said brake servo means comprising a fluidpressure cylinder, a piston in said cylinder cooperating therewith todefine a pressure release chamber and a pressure apply chamber, a fluidpressure source, conduit structurel interconnecting said pressure sourceand each chamber of said brake servo and connecting Ialso said sourcewith said clutch, fluid pressure distributor valve means in said conduitstructure for distributing pressure selectively from said source to saidclutch and to said brake servo chambers, said brake servo assuming areleased condition when both chambers thereof are pressurized andassuming an applied condition when one chamber Ithereof is pressurizedas the other chamber thereof is exhausted, a fluid pressure passagecommunicating with said other chamber, a portion of said fluid pressuredistributor valve means being disposed in said passage and adapted -toselectively pressurize and eX- haust the same, an accumulator valvesituated in said passage comprising a movable valve element and a valvechamber that receives said valve element, said chamber defining in pa-rtsaid passage, means for biasing said valve ele-ment to a passage closingposition, said piston developing a back pressure as said brake servobecomes applied,

said accumulator valve including pressure responsive means for urgingthe valve element to a passage opening yposition in response to apressure buildup in said other servo chamber and said passage, theapplication of said brake servo thereby being cushioned, and means forpressurizing said valve element to shift the same toward a passageopening position thereby rendering said accumulator valve inoperative.

3. In a control system for a power transmission mechanism adapted todeliver driving torque from a driving member to a driven member, gearelements forming plural torque delivery paths between said drivingmember and said driven member, fluid pressure operated servo means forcontrolling the relative motion of said gear elements, a fluid pressureoperated clutch actuated by one servo means for connecting together twoelements of said gearing to establish a high speed ratio condition,fluid pressure operated brake means actuated by said other servo meansfor anchoring an element of said gearing to establish a relatively lowspeed ratio condition, said brake servo means comprising a fluidpressure cylinder, a piston in said cylinder cooperating therewith todeline a pressure release chamber and a pressure apply chamber, a liuidpressure source, conduit structure interconnecting said pressure sourceand each chamber of said brake servo and connecting also sai-d sourcewith said clutch, said fluid pressure distributor valve means in saidconduit structure for distributing pressure selectively from said sourceto said clutch and to said brake servo chambers, said brake servoassuming a released condition when both chambers thereof are pressurizedan-d assuming an applied condition when the apply chamber thereof ispressurized and the release chamber thereof is exhausted, a fluidpressure passage communicating with said release chamber, a portion ofsaid liuid pressure distributor valve means being disposed in saidpassage and adapted to selectively pressurize and exhaust the same, anaccumulator valve situated in said passage comprising a movable valveelement and a valve chamber that receives said valve element, said valvechamber delining in part said passage, means for biasing said valveelement to a passage closing position, said piston developing a backpressure as said brake servo becomes applied, said accumulator valveincluding pressure responsive means for urging the valve element to apassageopening position in response to a pressure buildup in saidrelease servo chamber and said passage, the application of said brakeservo thereby being cushioned, means for pressurizing said valve elementto shift the same to a passage opening posi-tion thereby rendering saidaccumulator valve inoperative, and a oneway check valve means foraccommodating transfer of fluid through said passage means toward saidrelease chamber but inhibiting distribution of pressure through saidpassage means from said release chamber, said oneway check valve meansbypassing said accumulator valve as said brake means is released.

4. In a control system for a power transmission mechanism adapted todeliver driving torque from a driving member to a driven member, gearelements forming plural torque delivery paths between said drivingmember and said driven member, fluid pressure operated servo means forcontrolling the relative motion of said gear elements, a fluid pressureoperated clutch actuated by one servo means for connecting together twoelements of said gearing to establish a high speed ratio condition,liuid pressure operated brake means actuated by said other servo meansfor anchoring an element of said gearing to establish a relatively lowspeed ratio condition, said brake servo means comprising a fluidpressure cylinder, a piston in said cylinder cooperating therewith todefine a pressure release chamber and a pressure apply chamber, a fluidpressure source, conduit structure interconnecting said pressure sourceand each chamber of said brake servo and connecting also said sourcewith said clutch, fluid pressure distributor valve means in said conduitstructure for distributing pressure selectively from said source to saidclutch and to said brake servo chambers, said brake servo assuming areleased condition when both chambers thereof are pressurized andassuming an applied condition when one chamber thereof is pressurizedand the other chamber thereof is exhausted, a fluid pressure passagecommunicating with said other chamber, a portion of said lluid pressuredistributor valve means being disposed in said passage and adapted toselectively pressurize and exhaust the same, an accumulator valvesituated in said passage comprising a movable valve element and a valvechamber that receives said valve element, said valve chamber defining inpart said passage, means for biasing said valve element to a passageclosing position, said piston developing a back pressure as said brakeservo becomes applied, said accumulator valve including pressureresponsive means for urging the valve element to a passage openingposition in response to a pressure buildup in said other servo chamberand said passage, the application of said Ibrake servo thereby beingcushioned, a source of a pressure signal that is proportional inmagnitude to the torque delivered through said gearing, and means forestablishing fluid communication between said pressure source and saidaccumulator valve element thereby establishing a signal pressure forcethat opposes the influence of said spring means to modify theaccumulating action of said accumulator valve during a speed ratiochange in which said brake servo becomes applied.

5. In a control system for a power transmission mechanism adapted todeliver driving torque from a driving member lto a driven member, gearelements forming plural torque delivery paths between said drivingmember and said driven member, fluid pressure operated servo means forcontrolling the relative motion of said gear elements, a fluid pressureoperated clutch actuated by one servo means for connecting together twoelements of said gearing to establish a high speed ratio condition,fluid pressure operated brake means actuated by said other servo meansfor anchoring an element of said gearing to establish a relatively lowspeed ratio condition, said brake servo means comprising a fluidpressure cylinder, a piston in said cylinder cooperating therewith todeline a pressure release chamber and a pressure apply chamber, a fluidpressure source, conduit structure interconnecting said pressure sourceand each chamber of said brake servo and connecting also said sourcewith said clutch, liuid pressure distributor valve means in said conduitstructure for distributing pressure selectively from said source to saidclutch and to said brake servo chambers, said brake servo assuming areleased condition when both chambers thereof are pressurized andassuming an applied condition when one chamber thereof is pressurizedand the other chamber thereof is exhausted, a uid passage communica-tingwith said other chamber, a portion of said fluid pressure distributorvalve means being disposed in said passage and adapted to selectivelypressurize and exhaust the same, an accumulator valve situated in saidpassage comprising a movable valve element and a valve chamber thatreceives said valve element, said valve chamber defining in part saidpassage, means for biasing said valve element to a passage closingposition, said piston developing a back pressure as said brake servobecomes applied, said accumulator Valve including pressure responsivemeans for urging the valve element to a passage opening position inresponse to a pressure buildup in said other servo chamber and saidpassage, the application of said brake servo thereby being cushioned,means for pressurizing said valve element to shift the same to a passageopening position thereby rendering said `accumulator valve inoperative,a source of a pressure signal that is proportional in magnitude to thetorque delivered through said gearing7 and means for establishing liuidcommunication between said pressure source and said accumulator valveelement thereby establishing a signal pressure force that opposes theinfluence of said spring means to modify the accumulating action of saidaccumulator valve during a speed ratio change in which said brake meansbecomes applied.

6. In a control system for a power transmission mechanism adapted todeliver driving torque from a driving member to a driven member, gearelements forming plural torque delivery paths between said drivingmember and said driven member, fluid pressure operated servo means forcontrolling the relative motion of said gear elements, a liuid pressureoperated clutch actuated by one servo means for connecting together twoelements of said gearing to establish a high speed ratio condition,fluid pressure operated brake means actuated by said other servo meansfor anchoring an element of said gearing to establish a relatively lowspeed ratio condition, said brake servo means comprising a lluidpressure cylinder, a piston in said cylinder cooperating therewith todefine a pressure release chamber and a pressure apply chamber, a iiuidpressure source, conduit structure interconnecting said pressure sourceand each chamber of said brake servo and connecting also said sourceWith said clutch, fluid pressure distributor valve means in said conduitstructure for distributing pressure selectively from said source to saidclutch and to said brake servo chambers, said brake servo assuming areleased condition when both chambers thereof are pressurized andassuming an applied condition when one chamber thereof is pressurizedand the other chamber thereof is exhausted, a liuid pressure passagecommunicating with said other chamber, a portion of said iluid pressuredistributor valve means being disposed in said passage and adapted toselectively pressurize and exhaust the same, an accumulator valvesituated in said passage comprising a moveable valve element and a Valvechamber that receives said valve element, said valve chamber defining inpart said passage, means for biasing said valve element to a passageclosing position, said piston developing a back pressure as said brakeservo becomes applied, said accumulator valve including pressure re'-sponsive means for urging the valve element to a passage openingposition in response to a pressure buildup in said other servo chamberand said passage, the application of said brake servo thereby beingcushioned, means for pressurizing said Valve element to shift the sameto a passage opening position thereby rendering said accumulatorvalve'inoperative, a one-way check valve means for accommodatingtransfer of fluid through said passage means toward said other servochamber but inhibiting distribution of pressure through said passagemeans from said other servo chamber, said one-Way check valve meansbypassing said accumulator valve as said servo is released a source of apressure signal that is proportional in magnitude to the torquedelivered through said gearing, and means for establishing fluidcommunication between said pressure source and said accumulator valveelement thereby establishing a signal pressure force that opposes theiniiuence of said spring means to modify the accumulating action of saidaccumulator valve during a speed ratio change in which said servobecomes applied.

7. In a control system for a power transmission mechnism adapted todeliver driving torque from a driving member to a driven member, gearelements forming plural torque delivery paths between said drivenmemberl and said driven member, fluid pressure operated servo means forcontrolling the relative motion of said gear elements, a iluid pressureoperated clutch actuated by one servo means for connecting together twoelements of said gearing to establish a high speed ratio condition, Huidpressure operated brake means actuated by said other servo means foranchoring an element of said gearing to establish a relatively low speedratio condition, said brake servo means comprising a fluid pressurecylinder, a piston in said cylinder cooperating therewith to define apressure release chamber and a pressure apply chamber, a uid pressuresource, conduit structure interconnecting said pressure source and eachchamber of said brake servo and connecting also said source with saidclutch, uid pressure distributor valve means in said conduit structurefor distributing pressure selectively from said source to said clutchand to said brake servo chambers, said brake servo assuming a releasedcondition when both chambers thereof are pressurized and assuming anapplied condition when one chamber thereof is pressurized and the otherchamber thereof is exhausted, a fluid pressure passage communicatingwith said other chamber, a portion of said fluid pressure distributorvalve means being disposed in said passage and adapted to selectivelypressurize and exhaust the same, an accumulator valve situated in saidpassage comprising a movable valve element and a valve chamber thatreceives said valve element, said valve chamber defining in part saidpassage, means for biasing said valve element to a passage closingposition, said piston developing a back pressure as said brake servobecomes applied, said accumulator valve including pressure responsivemeans for urging the Valve element to a passage opening position inresponse to a pressure buildup in said other servo chamber and saidpassage, application of said brake servo thereby being cushioned, avehicle speed sensitive valve means for distributing pressure from ahigh pressure region of said circuit to said main regulator valve meansat low vehicle speeds thereby modifying regulating characteristics ofsaid regulator valve means to produce an increased control pressure, andmeans for establishing fluid communication between said accumulatorvalve and said speed sensitive valve means whereby an auxiliary pressureis imposed upon the former to augment the action of said spring meansthereby increasing the magnitude of the back pressure developed by saidbrake servo upon application thereof.

8. In a control system for a power transmission mechanism adapted todeliver driving torque from a driving member to a driven member, gearelements forming plural torque delivery paths between said drivingmember and said driven member, uid pressure operated servo means forcontrolling the relative motion of said gear elements, a fluid pressureoperated clutch actuated by one servo means for connecting together twoelements of said gearing to establish a high speed ratio condition,fluid pressure operated brake means actuated by said other servo meansfor anchoring an element of said gearing to establish a relatively lowspeed ratio condition, said brake servo means comprising a fluidpressure cylinder, a piston in said cylinder cooperating therewith todefine a pressure release chamber and a pressure apply chamber, a fluidpressure source, conduit structure interconnecting said pressure sourceand each chamber of said brake servo and connecting also said sourcewith said clutch, uid pressure distributor valve means in said conduitstructure for distributing pressure selectively from said source to saidclutch and to said brake servo chambers, said brake servo assuming Vareleased condition when both chambers thereof are pressurized andassuming an applied condition when one chamber thereof is pressurizedand the other chamber thereof is exhausted, a uid pressure passagecommunicating with vsaid other chamber, a portion of said fluid pressuredistributor valve means being disposed in said passage and adapted toselectively pressurize and exhaust the same, an accumulator valvesituated in said passage comprising a movable valve element and a valvechamber that receives said valve element, said valve chamber defining inpart said passage, means for biasing said valve element to a passageclosing position, said piston developing a back pressure as said brakeservo becomes applied, said accumulator valve including pressureresponsive means for urging the valve element to a passage openingposition in response to a pressure buildup in said other servo chamberand said passage, the application of said brake servo thereby beingcushioned, means for pressurizing said valve element to shift the sameto a passage opening position Vthereby rendering said accumulator valveinoperative, a vehicle speed sensitive valve means for distributingpressure from a high pressure region of said circuit to said mainregulator valve means at low vehicle speeds thereby modifying regulatingcharacteristics of said regulator valve means to produce an increasedcontrol pressure, and means for establishing fluid communication betweensaid accumulator valve and said speed sensitive valve means whereby anauxiliary pressure is imposed upon the former to augment the action ofsaid spring means thereby increasing the magnitude of the back pressuredeveloped by said brake servo upon application thereof.

9. In a control system for a power transmission mechanism adapted todeliver driving torque from a driving member to a driven member, gearelements forming plural torque delivery paths between said drivingmember and said driven member, fluid pressure operated servo means forcontrolling the relative motion of said gear elements, a fluid pressureoperated clutch actuated by one servo means for connecting together twoelements of said gearing to establish a high speed ratio condition,fluid pressure operated brake means actuated by said other servo meansfor anchoring an element of said gearing to establish a relatively lowspeed ratio condition, said brake servo means comprising a fluidpressure cylinder, a piston in said cylinder cooperating therewith todefine a pressure release chamber and a pressure apply chamber, a fluidpressure source, conduit structure interconnecting said pressure sourceand each chamber of said brake servo and connecting also said sourcewith said clutch, fluid pressure distributor valve means in said conduitstructure for distributing pressure selectively from said source to saidclutch and to said brake servo chambers, said brake servo assuming areleased condition when both chambers thereof are pressurized andassuming an applied condition when one chamber thereof is pressurizedand the other chamber thereof is exhausted, a fluid pressure passagecommuni-eating with said other chamber, a portion of said iluid pressuredistributor valve means being disposed in said passage and adapted toselectively pressurize and exhaust the same, an accumulator valvesituated in said passage comprising a movable valve element and a valvechamber that receives said valve element, said valve chamber defining inpart said passage, spring means for biasing said valve element to apassage closing position, said piston developing a back pressure as saidbrake servo becomes applied, said accumulator valve including pressureresponsive means for urging the valve element to a passage openingposition in response to a pressure buildup in said other servo chamberand said passage, the application of said brake servo thereby beingcushioned, means for pressurizing said valve element to shift the sameto a passage opening position thereby rendering said accumulator valveinoperative, a one-way check valve means for accommodating transfer offluid through said passage means toward said other servo chamber butinhibiting distribution of pressure through said passage means from saidother servo chamber, said one-way check valve means bypassing saidaccumulator valve as said brake servo is released, a vehicle speedsensitive valve means for distributing pressure from a high pressureregion of said circuit to said main regulator valve means at low vehiclespeeds thereby modifying regulating characteristics of said regulatorvalve means to produce an increased control pressure, and means forestablishing fluid communication between said accumulator valve and saidspeed sensitive valve means whereby an auxiliary pressure is imposedupon the former to augment the action of said spring means therebyincreasing the magnitude of the back pressure developed by said brakeservo upon application thereof.

10. In a control system for a power transmission mechanism adapted todeliver driving torque from a driving member to a driven member, gearelements forming plural torque delivery paths between said drivingmember and said driven member, fluid pressure operated servo means forcontrolling the relative motion of said gear elements, a fluid pressureoperated clutch actuated by one servo means for connecting together twoelements of said gearing to establish a high speed ratio condition,fluid pressure operated brake means actuated by said other servo meansfor anchoring an element of said gearing to establish a relatively lowspeed ratio condition, said brake servo means comprising a iluidpressure cylinder, a piston in said cylinder cooperating therewith todefine a pressure release chamber and a pressure apply chamber, a fluidpressure source, conduit structure interconnecting said pressure sourceand each chamber of said brake servo and connecting also said sourcewith said clutch, fluid pressure distributor valve means in said conduitstructure for distributing pressure selectively from said source to saidclutch and to said brake servo chambers, said brake servo assuming areleased condition when both chambers thereof are pressurized andassuming an applied condition when one chamber thereof is pressurizedand the other chamber thereof is exhausted, a fluid pressure passagecommunicating with said other chamber, a portion of said fluid pressuredistributor valve means being disposed in said passage and adapted toselectively pressurize and exhaust the same, an accumulator valvesituated in said passage comprising a movable valve element and a valvechamber that receives said valve element, said valve chamber defining inpart said passage, spring means for biasing said valve element to apassage closing position, said piston developing a back pressure as saidbrake servo becomesrapplied, said accumulator valve including pressureresponsive means forurging the valve element to a passage openingposition in response to a pressure buildup in said other servo chamberand said passage, the application of said brake servo thereby beingcushioned, a vehicle speed sensitive valve means for distributingpressure from a high pressure region of said circuit to said mainregulator valve means at low vehicle speeds thereby modifying regulatingcharacteristics of said regulator valve means to produce an increasedcontrol pressure, means for establishing fluid communication betweensaid accumulator valve and said speer sensitive valve means whereby anauxiliary pressure is imposed upon the former to augment the action ofsaid spring means thereby increasing the magnitude of the back pressuredeveloped by said brake servo upon application thereof, a source of apressure signal that is proportional in magnitude to the torquedelivered through said gearing, and means for establishing fluidcommunication between said pressure source and said accumulator valveelement thereby establishing a signal pressure force that opposes theiniluence of said spring means to modify the accumulating action of saidaccumulator valve during a speed ratio change in which said brake servobecomes applied.

11. In a control system for a power transmission mechanism adapted todeliver driving torque from a driving member to a driven member, gearelements forming plural torque delivery paths between said drivingmember and said driven member, fluid pressure operated servo means forcontrolling the relative motion of said gear elements, a fluid pressureoperated clutch actuated by one servo means for connecting together twoelements of said gearing to establish a high speed ratio condition,fluid pressure operated brake means actuated by said other servo meansfor anchoring an element of said gearing to establish a relatively lowspeed ratio condition, said brake servo means comprising a fluidpressure cylinder, a piston in said cylinder cooperating therewith todene a pressure release chamber and a pressure apply chamber, a fluidpressure source, conduit structure interconnecting said pressure sourceand each chamber of said brake servo and connecting also said sourcewith said clutch, fluid pressure distributor valve means in said conduitstructure for distributing pressure selectively from said source to saidclutch and to said brake servo chambers, said brake servo assuming areleased condition when both chambers thereof are pressurized andassuming an applied condition when one chamber thereof is pressurizedand the other chamber thereof is exhausted, a fluid pressure passagecommunicating with said other chamber, a portion of said fluid pressuredistributor valve means being disposed in said passage and adapted toselectively pressurize land exhaust the same, an accumulator valvesituated in said passage comprising a movable valve element and a valvechamber that receives said valve element, said valve chamber defining inpart said passage, spring means for biasing said valve element to -apassage closing position, said piston developing a back pressure as saidbrake servo becomes applied, said accumulator valve including pressureresponsive means for urging the valve element to a passage openingposition in response to -a pressure buildup in said other servo chamberand .said passage, the application of said brake servo thereby beingcushioned, means for pressurizing said valve element to shift the sameto a passage opening position thereby 'rendering said accumulator valveinoperative, a vehicle speed sensitive cutback valve means fordistributing pressure from a high pressure region of said circuit tosaid main regulator valve means at low vehicle speeds thereby modifyingregulating characteristics of said regulator valve means to produce anincreased control pressure, means for establishing uid communicationbetween said accumulator valve and said cutback valve means whereby anauxiliary pressure is imposed upon the former to augment the action ofsaid spring means thereby increasing the magnitude of the back pressuredeveloped by said intermediate servo upon application of .said brakeservo, a source of a pressure signal that is proportional in magnitudeto the torque delivered through said gearing, and means for establishingfluid communication between said pressure source and said accumulatorvalve element thereby establishing a signal pressure force that opposesthe influence of said spring means to modify the accumulating action ofsaid accumulator valve during a speed ratio change in which said brakeservo becomes applied.

12. In a control system for a power transmission mechanism adapted todeliver driving torque from a driving member to a driven member, gearelements forming plural torque delivery paths between said drivingmember and said driven member, uid pressure operated servo means forcontrolling the relative motion of said gear elements, a iluid pressureoperated clutch actuated by one servo means for connecting together twoelements of said gearing to establish a high speed ratio condition,fluid pressure operated brake means actuated by said other servo meansfor anchoring an element of said gearing to establish a relatively lowspeed ratio condition, said brake .servo means comprising a fluidpressure cylinder, a piston in said cylinder cooperating therewith todefine a pressure release chamber and a pressure apply chamber, a fluidpressure source, conduit structure interconnecting said pressure sourceand each chamber of said brake servo and connecting also said sourcewith said clutch, uid pressure distributor valve means in said conduitstructure for distributing pressure selectively from said source to saidclutch and to said brake servo chambers, said lbrake servo assuming areleased condition when both chambers thereof are pressurized andassuming an applied condition when one chamber thereof is pressurizedand the other chamber thereof is exhausted, a iluid pressure passagecommunicating with said other chamber, a portion of said fluid pressuredistributor valve means being disposed in said passage and adapted toselectively pressurize and exhaust the same, an accumulator valvesituated in said passage comprising a movable valve element and a valvechamber that receives said valve element, said valve chamber defining inpart said passage, spring means for biasing said valve element to apassage closing position, said piston developing a back pressure as saidbrake servo becomes applied, said accumulator valve including pressureresponsive means for urging the valve element to a passage openingposition in response to a pressure buildup in said other servo chamberand said passage, the application of said brake servo thereby beingcushioned, means for pressurizing said valve element to shift the sameto a passage opening position thereby rendering said accumulator valveinoperative, a one-way check valve means for accommodating transfer ofiluid through said passage means toward said other servo chamber butinhibiting distribution of pressure through said passage means from saidother servo chamber, said one-way check valve means bypassing saidaccumulator valve as said intermediate brake band is released, a vehiclespeed sensitive valve means for distributing pressure from a highpressure region of said circuit to said main regulator valve means atlow vehicle speeds thereby modifying regulating characteristics of saidregulator valve means to produce an increased control pressure, meansfor establishing lluid communication between said accumulator valve andsaid speed sensitive valve means whereby an auxiliary pressure isimposed upon the former to augment the action of said spring meansthereby increasing the magnitude of the back pressure developed by saidbrake servo upon application thereof, a source of a pressure signal thatis proportional in magnitude to the torque delivered through saidgearing, and means for establishing fluid communication between saidpressure source and said accumulator valve element thereby establishinga signal pressure force that opposes the influence of said spring tomodify the accumulating action of said accumulator valve during a speedratio change in which said brake servo becomes applied.

References Cited UNITED STATES PATENTS 2,893,261 7/1959 Flinn 74-7522,971,405 2/1961 Flinn 74-752 2,987,942 6/1961 Jania 74-752 3,027,7834/1962 Kelley 74-752 3,080,764 3/1963 Miller et al. 74-15.84 3,085,4494/ 1963 De Corte et al. 74-752 3,091,980 6/1963 Black 74-752 3,099,1727/1963 .Tania et al. 74-751 3,132,535 5/1964 Borman et al 74-6883,142,999 8/ 1964 Searles et al. 74-472 DONLEY J. STOCKING, PrimaryExaminer. DAVID I. WILLIAMOWSKY, Examiner. I., R. BENEFIEL, AssistantExaminer,

8. IN A CONTROL SYSTEM FOR A POWER TRANSMISSION MECHANISM ADAPTED TODELIVER DRIVING TORQUE FROM A DRIVING MEMBER TO A DRIVEN MEMBER, GEARELEMENTS FORMING PLURAL TORQUE DELIVERY PATHS BETWEEN SAID DRIVINGMEMBER AND SAID DRIVEN MEMBER, FLUID PRESSURE OPERATED SERVO MEANS FORCONTROLLING THE RELATIVE MOTION OF SAID GEAR ELEMENTS, A FLUID PRESSUREOPERATED CLUTCH ACTUATED BY ONE SERVO MEANS FOR CONNECTING TOGETHER TWOELEMENTS OF SAID GEARING TO ESTABLISH A HIGH SPEED RATIO CONDITION,FLUID PRESSURE OPERATED BRAKE MEANS ACTUATED BY SAID OTHER SERVO MEANSFOR ANCHORING AN ELEMENT OF SAID GEARING TO ESTABLISH A RELATIVELY LOWSPEED RATIO CONDITION, SAID BRAKE SERVO MEANS COMPRISING A FLUIDPRESSURE CYLINDER, A PISTON IN SAID CYLINDER COOPERATING THEREWITH TODEFINE A PRESSURE RELEASE CHAMBER AND A PRESSURE APPLY CHAMBER, A FLUIDPRESSURE SOURCE, CONDUIT STRUCTURE INTERCONNECTING SAID PRESSURE SOURCEAND EACH CHAMBER OF SAID BRAKE SERVO AND CONNECTING ALSO SAID SOURCEWITH SAID CLUTCH, FLUID PRESSURE DISTRIBUTOR VALVE MEANS IN SAID CONDUITSTRUCTURE FOR DISTRIBUTOR PRESSURE SELECTIVELY FROM SAID SOURCE TO SAIDCLUTCH AND TO SAID BRAKE SERVO CHAMBER, SAID BRAKE SERVO ASSUMING ARELEASED CONDITION WHEN BOTH CHAMBERS THEREOF ARE PRESSURIZED ANDASSUMING AN APPLIED CONDITION WHEN ONE CHAMBER THEREOF IS PRESSURIZEDAND THE OTHER CHAMBER THEREOF IS EXHAUSTED, A FLUID PRESSURE PASSAGECOMMUNICATING WITH SAID OTHER CHAMBER, A PORTION OF SAID FLUID PRESSUREDISTRIBUTOR VALVE MEANS BEING DISPOSED IN SAID PASSAGE AND ADAPTED TOSELECTIVELY PRESSURIZE AND EXHAUST THE SAME, AN ACCUMULATOR VALVESITUATED IN SAID PASSAGE COMPRISING A MOVABLE VALVE ELEMENT AND A VALVECHAMBER THAT RECEIVES SAID VALVE ELEMENT, SAID VALVE CHAMBER DEFINING INPART SAID PASSAGE, MEANS FOR BIASING SAID VALVE ELEMENT TO A PASSAGECLOSING POSITION, SAID PISTON DEVELOPING A BACK PRESSURE AS SAID BRAKESERVO BECOMES APPLIED, SAID ACCUMULATOR VALVE INCLUDING PRESSURERESPONSIVE MEANS FOR URGING THE VALVE ELEMENT TO A PASSAGE OPENINGPOSITION IN RESPONSE TO A PRESSURE BUILDUP IN SAID OTHER SERVO CHAMBERAND SAID PASSAGE, THE APPLICATION OF SAID BRAKE SERVO THEREBY BEINGCUSHIONED, MEANS FOR PRESSURIZING SAID VALVE ELEMENT TO SHIFT THE SAMETO A PASSAGE OPENING POSITION THEREBY RENDERING SAID ACCUMULATOR VALVEINOPERATIVE, A VEHICLE SPEED SENSITIVE VALVE MEANS FOR DISTRIBUTINGPRESSURE FROM A HIGH PRESSURE REGION OF SAID CIRCUIT TO SAID MAINREGULATOR VALVE MEANS AT LOW VEHICLE SPEEDS THEREBY MODIFYING REGULATINGCHARACTERISTICS OF SAID REGULATOR VALVE MEANS TO PRODUCE AN INCREASEDCONTROL PRESSURE, AND MEANS FOR ESTABLISHING FLUID COMMUNICATION BETWEENSAID ACCUMULATOR VALVE AND SAID SPEED SENSITIVE VALVE MEANS WHEREBY ANAUXILIARY PRESSURE IS IMPOSED UPON THE FORMER TO AUGMENT THE ACTION OFSAID SPRING MEAS THEREBY INCREASING THE MAGNITUDE OF THE BACK PRESSUREDEVELOPED BY SAID BRAKE SERVO UPON APPLICATION THEREOF.